Detonation problem

[KiltedBanshees93GT]

Well, I've decided that my car hates me . Lately I've noticed that shes started knocking, lightly at first, but its gotten worse as time went on. It only occurs (that I've been able to tell) at lower rpm, 1500 and below,when going uphill. if I drop a gear and get the rpm back up toward 2k it seems to stop or diminish to the point I cant hear it over the exhaust. The big thing I dont get is that I've had to get on it a few times, and it doesent seem to knock on heavy throttle, just at lower rpm while going uphill.
I've had the car for like 7 years and never had any problems like this. Timing is at the factory 10degrees, I've tried higher octane (helps but doesent fix), run 2 bottles of fuel system cleaner (didnt make that much difference), car is running at normal temp, etc.
I know the car needs a tune up, which I'll do this weekend if the temps come up a bit, but can anyone think of anything else to look at? Dirty fuel filter maybe? I havent changed that in a good while.

Between this and the tranny starting to whine, it seems like I'll never get her back to 100%

Help,
J